Papers by Keyword: Calcium Orthophosphate

Abstract: Heat-resistant properties of the cement stone are provided by both high-temperature filler and the modified matrix on the basis of the Portland cement. For production of heat-resistant compositions as high-temperature filler, it is offered to use the secondary and accompanying products of production of carbide of silicon (SiC) and production wastes of the abrasive tools on a ceramic base. Increase in heat-resistant properties of the Portland cement knitting substance is offered to be solved by introduction to the structure of a cement composition of single substituted orthophosphate of calcium. The choice as an additive to the Portland cement a single substituted orthophosphate of calcium (double superphosphate) is proved by questions of safety measures and ecology, when using ortho-phosphoric acid and its salts for giving to cement compositions heat-resistant properties. The multicomponent composition of fine-grained concrete makes it possible to operate effectively the processes of forming the structure of cement stone at all stages of the technology, and to obtain materials with the most diverse set of properties. An introduction to the structure of a composite of 5% of filler of cyclonic dust of carbide of silicon, and a replacement of quartz filler by waste of abrasive production gave the increase of the compressive strength at 12%, bending strength for 36%. The thermal firmness increased by 3 times. An introduction to the structure of heat-resistant composition of single substituted orthophosphate of calcium (double superphosphate) in a number of 0.2% of the mass of cement allowed to increase the thermal firmness of structures to 20 heat exchanges (water, 800 oС).

Abstract: Amorphous calcium phosphates (ACPs) represent a unique class of biomedically relevant calcium orthophosphate salts, in which there are neither translational nor orientational long-range orders of the atomic positions. Nevertheless, the constancy in their chemical composition over a relatively wide range of preparation conditions suggests the presence of a well-defined local structural unit, presumably, with the structure of Ca9(PO4)6 – so-called Posner’s cluster. ACPs have variable chemical but rather identical glass-like physicochemical properties. Furthermore, all ACPs are thermodynamically unstable compounds and, unless stored in dry conditions or doped by stabilizers, spontaneously they tend to transform to crystalline calcium orthophosphates. Although some order within general disorder is the most distinguishing feature of ACPs, the solution instability of ACPs and their easy transformation to crystalline phases might be of a great biological relevance. Namely, the initiating role ACPs play in matrix vesicle biomineralization raises the importance of this phase from a mere laboratory curiosity to that of a key intermediate in skeletal calcification. Furthermore, ACPs are very promising candidates to manufacture artificial bone grafts.

Abstract: Ceramics used for the repair and reconstruction of diseased or damaged parts of the musculo-skeletal system, termed bioceramics, can be bioinert, bioresorbable and bioactive, as well as porous for tissue ingrowth. This review is devoted to calcium orthophosphates, which belong to the categories of bioresorbable and bioactive bioceramics. There have been a number of major advances made in this field during the past 30 – 40 years. From initial work on development of bioceramics that were tolerated in the physiological environment, emphasis has now shifted towards the use of bioceramics that interact with bone tissue by forming a direct bond. By structural and compositional control, it is now possible to choose whether the bioceramics of calcium orthophosphates are biologically stable once incorporated within the skeletal structure or whether they are resorbed over time. Current biomedical applications of calcium orthophosphate bioceramics include replacements for hips, knees, teeth, tendons and ligaments, as well as repair for periodontal disease, maxillofacial reconstruction, augmentation and stabilization of the jawbone, spinal fusion and bone fillers after tumor surgery.

Abstract: There has been much recent activity in the research area of nanoparticles and nanocrystalline materials, in many fields of science and technology. This is due to their outstanding and unique physical, mechanical, chemical and biological characteristics. Recent developments in biomineralization have demonstrated that nano-sized particles play an important role in the formation of the hard tissues of animals. It is well established that the basic inorganic building blocks of bones and teeth of mammals are nano-sized and nanocrystalline calcium orthophosphates (in the form of apatites) of a biological origin. In mammals, tens to hundreds of nanocrystals of biological apatite are found to combine into self-assembled structures under the control of bio-organic matrixes. It was also confirmed experimentally that the structure of both dental enamel and bones could be mimicked by an oriented aggregation of nano-sized calcium orthophosphates, determined by the biomolecules. The application and prospective use of nano-sized and nanocrystalline calcium orthophosphates for clinical repair of damaged bones and teeth are also known. For example, a greater viability and a better proliferation of various cells were detected on smaller crystals of calcium orthophosphates. Furthermore, studies revealed that the differentiation of various cells was promoted by nano-sized calcium orthophosphates. Thus, the nano-sized and nanocrystalline forms of calcium orthophosphates have the potential to revolutionize the field of hard tissue engineering, in areas ranging from bone repair and augmentation to controlled drug delivery devices. This paper reviews the current state of knowledge and recent developments of various nano-sized and nanocrystalline calcium orthophosphates, covering topics from the synthesis and characterization to biomedical and clinical applications. This review also provides possible directions of future research and development.